iC-TW3 SENSOR SIGNAL CONDITIONER WITH
TEMPERATURE COMPENSATION AND LINE DRIVER
Rev B1, Page 19/24
TEMPERATURE SENSING
CCELSIUS(3:0)
Adr 0x05; Bit 3:0
R/W
iC-TW3 contains an on-chip temperature sensor. Op-
tionally, an external sensor can be used by setting bit
XCELSIUS of register 0x02 to 1. An external temper-
ature sensor is useful for remote temperature sensing
or in situations where the internal sensor does not pro-
vide adequate accuracy. Also, device self-heating due
to heavy output loads can have an impact on the inter-
nal sensor readings. Connect the external temperature
sensor with its analog output to pin KELVIN.
Code
1111
...
Bit 3 is sign, bits 2:0 are magnitude of correction
most negative correction
...
1001
1000
0000
0001
...
least negative correction
no correction
no correction (default)
least positive correction
...
0111
most positive correction
Table 34: Coarse offset correction
XCELSIUS
Adr 0x02; Bit 6
Function
R/W
Code
FCELSIUS(3:0)
Adr 0x05; Bit 7:4
R/W
0
1
Select internal temperature sensor (default)
Select external temperature sensor
Code
0000
0001
...
Value added to ADC reading is FCELSIUS(3:0) - 8
-8 (default)
-7
...
7
Table 33: Temperature sensor select
1111
Table 35: Fine offset correction
An ADC converts the analog temperature signal into
an 8-bit digital word. In case the on-chip sensor is used
the 8-bit value spans a temperature range of -50 °C to
150 °C. It is recommended to calibrate the ADC using
register 0x05 even when using an external tempera-
ture sensor.
CELSIUS(7:0)
Adr 0x12; Bit 7:0
R
Data
0x00
Function
Current temperature ADC value that is used for
compensation calculations. Value of this register is
0x40 + FCELSIUS(3:0) - 8
0xFF
Table 36: Temperature data
Calibrating the temperature ADC
Temperature alarm
The raw ADC value can be accessed through register
0x40. A ±2 increment hysteresis is applied to the ADC
value to remove conversion noise and the offset regis-
ter 0x05 is added. The final value is stored in register
0x12 and is used for temperature compensation.
The iC-TW3 features a built-in temperature alarm sys-
tem. An alarm threshold can be specified by the user
via the TALARM(2:0) bits in register 0x03. A tempera-
ture alarm is asserted once the temperature value gen-
erated by the ADC is above the defined threshold. The
alarm is indicated by the ERR_TEMP bit set to 1 as
well as by pin NERR going low.
To achieve best temperature accuracy it is required to
calibrate the ADC by correctly programming register
0x05. At any known ambient temperature the register
0x05 is programmed such to read the expected ADC
value. As an example, consider the product assem-
bly floor with an ambient temperature of 20 °C. Due to
device variation the ADC value read before calibration
can be anything between 0 °C to 40 °C. Register 0x05
is now used to tune the ADC output value to the correct
binary representation of 20 °C.
TALARM(2:0)
Adr 0x03; Bit 4:2
R/W
Code
000
001
...
tempthreshold = (TALARM(2:0) x 16) + 144
144 (default)
160
...
110
111
240
Alarm disabled
Table 37: Temperature alarm threshold
ICHAUS [ IC-HAUS GMBH ]
